The present invention relates to an internal combustion engine common-rail injection system with a fuel premetering device.
As is known, in modern internal combustion injection engines, each injector is supplied with high-pressure fuel by a common header or so-called xe2x80x9ccommon railxe2x80x9d, which is supplied by a high-pressure, normally piston, pump in turn supplied with fuel from the fuel tank by a low-pressure pump. The high-pressure pump supplies the common rail with fuel at a pressure controlled by a pressure regulating or fuel premetering device normally comprising a valve controlled by an electromagnet, i.e. a solenoid valve, which, when closed, supplies the common rail with all the fuel pumped by the high-pressure pump, and, when opened partly or fully, drains the fuel pumped in excess along a drain conduit back into the tank.
In known technology, the regulating device valve comprises a shutter, which is kept in the closed position by the armature of the electromagnet when this is energized, and which is kept in the open position by a spring when the electromagnet is deenergized. The electromagnet is energized by a current ranging between zero and a predetermined value to open the valve partly and regulate the pressure of the fuel supplied to the common rail.
The above method has various drawbacks. In particular, to keep the valve closed, the electromagnet must be supplied with the maximum excitation current, so that a high current must be varied to open the valve partly to regulate the fuel pressure. Moreover, if the electromagnet fails to be energized during operation of the engine, the valve is opened fully by the spring, thus draining the common rail completely and arresting the engine. Finally, when the electromagnet is energized by a low current to begin closing the valve, the friction-induced resistance to motion of the armature represents a far from negligible component part of total resistance, making fine fuel pressure adjustment difficult to achieve.
It is an object of the present invention to provide an internal combustion engine common-rail injection system with a fuel premetering device, which provides for a high degree of reliability, is cheap to produce, and eliminates the aforementioned drawbacks typically associated with known injection systems.
According to the present invention, there is provided a common-rail injection system for an internal combustion engine, having a fuel premetering device comprising a valve controlled by an electromagnet; said valve being located between a delivery conduit of a high-pressure pump supplying a common rail, and a drain conduit for draining surplus fuel; characterized in that said valve is normally closed by elastic means; said electromagnet being energized to open said valve in opposition to said elastic means.
More specifically, the electromagnet is energized by a current varying in response to the operating conditions of said engine, so that premetering is self-adaptive.